Tumor therapy with heavy ions has come to be an established method for treating tissue, for example, tumor diseases, over the course of recent decades. However, the experience gained thereby is also applied in purely technical areas.
A common feature of all known methods is that a focused particle beam provided by an accelerator is conducted to one or more radiation or treatment rooms by means of a high energy beam transport system. In the radiation room, a target volume to be irradiated is positioned, and irradiated with the particle beam.
It is known that a target volume to be irradiated can move. For example, a lung tumor which moves as the patient breathes may be located in the target volume. For the purpose of investigating the effect the motion has on the treatment success of the particle therapy, however, the motion can also be simulated by means of non-living model bodies referred to as phantoms.
It is a particular challenge in the context of particle therapy to achieve the most homogeneous distribution possible of the radiation dose deposited in the tissue. One reason for which homogeneous dose distribution in the target volume is of particular interest is the fact that the cells of the tumor located in the target volume only die with adequate reliability at or above a threshold dose, while at the same time, excessive radiation burden to the surrounding healthy tissue should be avoided. Thus, in irradiation methods in which a plurality of individual radiation doses are to be successively deposited in various target points in the target volume, which is to say with a scanned particle beam, it is still difficult to achieve this desired homogeneous dose distribution in the target volume if the target volume moves during radiation. Improvement of the homogeneity of dose distribution in target volumes thus remains the subject of current research.
For example, in the case of a scanned particle beam, one possibility is to distribute the radiation dose to be applied over several passes, which is called “rescanning.” In this method, the target points of the target volume are approached multiple times so that the total dose to be applied is built up successively by multiple individual doses applied repeatedly during the rescanning passes. Repeatedly approaching the target points with individual doses allows for a statistical averaging over the individual doses, by which means any incorrectly deposited doses can be averaged, statistically speaking. Motions of the target volume can be at least partly compensated for in this way.
Nevertheless, in this process each target point is approached multiple times with an appropriately reduced sub-dose, which can cause radiation by rescanning to take a substantial additional amount of time, since the extraction rate must be reduced in accordance with the reduced sub-dose. It is the state of the art that it is necessary to put up with a prolonged radiation process in order to increase the homogeneity of the dose distribution and thus, in the case of radiotherapy, to improve the treatment success.
In addition, it is known to track the motion of the target volume and to take this into account in calculating the individual doses.